The present invention relates to methods for preparing compounds of the thiazolo[3,4,5-de] [4,1]benzothiazepine type and in particular of 2-imino-9-trifluoromethyl-4,5-dihydro-2H,7H-thiazolo[3,4,5-de] [4,1]benzothiazepine 6,6-dioxide methanesulfonate and of (R,S)-2-imino-9-trifluoromethyl-4,5-dihydro-2H,7H-thiazolo[3,4,5-de] [4,1]benzothiazepine 6-oxide and these enantiomers and their pharmaceutically acceptable salts. These products are described in patent application WO 99/05147. These products are known and are particularly useful for the treatment and/or prevention of convulsions and diseases linked to glutamatergic transmission. They are especially useful for treating and/or preventing ischemias (such as focal or global ischemia) following cerebral vascular accidents such as thromboembolic and hemorrhagic stroke, cardiac arrest, arterial hypotension, cardiac, vascular or pulmonary surgery or severe hypoglycemia, in the treatment of the effects caused by anoxia, whether it is perinatal or subsequent to drowning, a high pressure or cerebrospinal lesions, for treating or preventing the progression of neurodegenerative diseases, HUNTINGTON's chorea, of ALZHEIMER's disease and other dementias, of amyotrophic lateral sclerosis or of other motor neurone diseases, of olivopontocerebella atrophy and of PARKINSON's disease, against epileptogenic (epilepsy) and/or convulsive manifestations, for the treatment of cerebral or spinal traumas, of traumas linked to degeneration of the inner ear or of the retina, of tinnitus, of anxiety, of depression, of schizophrenia, of TOURETTE's syndrome, of hepatic encephalopathies, of sleep disorders, of attention deficit disorders, of disorders of hormonal conditions (excess secretion of GH or LH, secretion of corticosterone), as analgesics, anti-inflammatory agents, antianorectics, antimigraine drugs, antiemetics and for treating poisoning by neurotoxins and neurological disorders associated with viral diseases such as meningitis and viral encephalitis, AIDS, rabies, measles and tetanus. These compounds are useful for the prevention of, tolerance to and dependency on the symptoms of withdrawal from drugs and alcohol, and of inhibition of addiction to and dependence on opiates, barbiturates, amphetamine and benzodiazepines. They may also be used in the treatment of deficiencies linked to mitochondrial abnormalities such as mitochondrial myopathy, LEBER's syndrome, WERNICKE's encephalopathy, RETT's syndrome, homocysteinemia, hyperprolinemia, hydroxybutyric-aminoaciduria, saturine encephalopathy (chronic lead poisoning) and sulfite oxidase deficiency.